1. Field of the Invention
The present invention relates generally to thermal protectors and more specifically to a self heating thermal protector for use in protecting recessed incandescent lighting fixtures.
2. Background of the Invention
Recessed fixtures provide architecturally desirable illumination in homes, offices and commercial buildings. Offices and commercial buildings are generally designed for hung ceilings to accommodate electrical conduit and heating and ventilating ducts. In the past the space above the ceiling has been either empty or filled with the aforementioned equipment with air spaces between the equipment. Under these conditions the greatest danger has been overlamping, a condition which exists when a lamp of larger wattage than the fixture is rated for is installed in the fixture. When a larger wattage lamp is used, the heat generated in the fixture is not dissipated quickly enough and the fixture temperature increases to a level that is higher than intended by the fixture designer. If the fixture is operated with the larger lamp, the resulting fixture temperature will rise to a point where charring of plastic parts and wire insulation within and about the fixture can occur. Eventually, deterioration of the fixture components may result in a fire. Fires from overheated lighting fixtures have caused extensive property damage.
Currently, because of increased concern with energy conservation, local and federal agencies are sponsoring programs in which homes and commercial buildings are being insulated as they are built. Existing homes and commercial buildings are normally insulated by forcing thermal insulation into the spaces which are to be insulated.
Building codes require that a barrier be constructed around recessed fixtures to prevent thermal insulation from coming into contact with the fixture. For new structures the foregoing requirement is costly but feasible. The installation of barriers around recessed fixtures in existing structures is relatively expensive and difficult to achieve.
Materials used in the construction of recessed fixtures are thermally rated for the application. Such materials are lamps, sockets, wire and insulation to name a few. The overheating problem due to overlamping and of thermal insulation installed in contact with the fixture exists with all type of fixtures but may be particularly serious with respect to recessed incandescent fixtures.
The possibility of relying upon the heat generated by the lamp in its fixture and its rate of dissipation as an indicator of safe operation has been considered. However, because of the variety of fixtures and lamp sizes and the cost involved of adapting a thermal protector to each specific application, a universal solution of using a self heating thermal protector described herein is proposed.
Safe operation of a recessed fixture depends upon the fixture dissipating a predetermined quantity of heat to its surroundings. The required heat flow is obtained by the air in contact with the fixture removing the heat. The air in contact with the fixture will heat up as it absorbs heat and the heated air, being lighter, rises allowing cooler air to flow in. This continual movement of air dependably cools the fixture. If air movement is restricted by thermal insulation, heat build up will occur resulting in a dangerous situation.
The present invention is a self heating thermal protector for controlling the flow of current to a lighting fixture by measuring the rate of heat flow from a dedicated heat source located in close proximity to the incandescent light fixture. Current is permitted to flow to the lighting fixture when the temperature of the self heating thermal detector is sufficient to avoid deterioration of electrical components such as plastic parts and wire insulation in the associated lighting fixture. The thermal detector interrupts the flow of current to the associated fixture when the temperature of the self heating thermal protector increases to a temperature that is not safe.
Specifically, the self heating thermal protector of the present invention uses a resistor as a heat source, a bimetallic element as a switch located within a thermally conducting enclosure located proximate the heat source for controlling the flow of current to a lighting fixture and thermally conductive potting compound which encapsulates both the heat source and the bimetallic element. The potting compound provides good thermal conductivity between the resistor, the bimetallic element and the surrounding air. A mounting member for mounting the thermal detector to a junction box is composed of thermally insulating material and provides dual functions, one of mounting the thermal detector to a junction box, and a second of thermally isolating the thermal protector from the junction box.
The foregoing has outlined, rather broadly, the preferred feature of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention and that such other structures do not depart from the spirit and scope of the invention in its broadest form.